This invention relates to a sled-guide-assembly, in particular of an optical attenuating device. This invention also relates to a sled for such a sled-guide-assembly.
Optical attenuating devices are used for attenuating optical signals, e.g. for measurement, test, calibration or adjustment purposes. The optical attenuating device generally comprises an optical attenuating element arranged in the light-path of the optical signal. An attenuator with variable attenuation is disclosed e.g. in EP-A-55742, wherein attenuation effect depends of the position of a movable attenuating element with respect to the light-path.
It is an object of the present invention to provide an improved variable optical attenuator. The object is solved by the independent claims. Preferred embodiments are shown by the dependent claims.
According to the design of such an optical attenuating element, the attenuating effect depends of the longitudinal position of the attenuating element with respect to the light-path. In an optical attenuating device according to the invention, a sled-guide-assembly is used for positioning the optical attenuating element with respect to the light-path. The sled-guide-assembly preferably comprises a guidance extending transversally to the light-path, and a sled, which is movable along the guidance. The sled supports the optical attenuating element. To achieve good measurement results, the optical attenuating element and therefore the sled in the guidance can be positioned preferably with very high precision.
In one embodiment, the optical attenuating element is made of a first material, e.g. glass, the sled is manufactured of a second material, e.g. a synthetic or plastic material, and the guidance is made of a third material, e.g. aluminum or aluminum alloy. The sled-guide-assembly may be provided for use in a wide range of temperatures. The different materials of sled, optical attenuating element and guidance have usually different coefficients of thermal expansion. Therefore, varying temperatures may lead to thermal stress deforming the sled. Deformation of the sled, however, may increase friction and may end in clamping or squeezing between sled and guidance.
According to the invention, the sled is provided with first and second edges overlapping guide rails of the guidance transversally with respect to the longitudinal direction of the guide rails. The first or the second edges are formed flexible or spring elastic and are arranged in such a way abutting with bias or prestress against the guide rails. Biasing or stressing the respective edges against the guide rails leadsxe2x80x94on the one handxe2x80x94to compensation of play or clearances provided in the direction of the bias or stress between the edges and the guide rails and therefore between the sled and the guidance. Relative movements between sled and guidance according to clearances are thus reduced or eliminated in stress direction. On the other hand biasing or stressing compensates relative movements between the edges and the guide rails as result of thermal deformation of the sled. Therefore, high precision positioning of the sled relative to the guidance can be provided. In a preferred use of the sled-guide-assembly guide assembly in an optical attenuator, high precision positioning of the optical attenuating element relative to the light-path can be provided. Also, high precision positioning of the sled can be enabled over a wide range of temperatures.
In a preferred embodiment the sled is divided in its longitudinal direction into a leading sled part and a trailing sled part both fixed independently of each other to the object, which is supported by the sled. Dividing the sled allows de-coupling thermal expansion of the object from thermal expansion of the sled. Thus, thermal deformations of the sled can be reduced or even eliminated. In combination with the biased or stressed abutment between sled and guidance, positioning with very high precision can be achieved.
In another embodiment, the sled parts are coupled to each other via common second edges, wherein this second edges are the flexible ones. This allows simplifying manufacturing of the sled.
In a further embodiment, the flexible edges are formed in a way that they abut point-shaped or line-shaped against the guide rails. The other edges abut plane-shaped against the guide rails. Thus, the functions of the edges can be strictly separated. The flexible edges are provided for stressing or biasing the edges against the guide rails and the other edges are provided for guiding or gliding the sled along the guidance. Therefore friction between sled and guidance is reduced and alignment between sled and guidance is improved.
In another preferred embodiment, each common second edge is provided with a curvature, which is convex to the respective guide rail, extends in the longitudinal direction of the sled substantially over the entire length of the respective second edge and abuts with tension against the respective guide rail, preferably in the middle of the respective edge with respect to the longitudinal direction of the sled. The elasticity of the material of the edges is used to form a spring-like flexibility of the edges.